A embodiment of the present invention relates to a laminate that encloses a transfer layer and includes polycarbonate, a method for manufacturing the laminate, and an identification medium including the laminate, in particular, an identification medium such as a card or a passport.
A laminated material, or a laminate, of an identification medium, such as a card or a passport, that encloses a transfer layer is highly resistive against chemical agents, wear, and tampering and is difficult to remove by unauthorized means, as compared with other structures in which the transfer layer is located on the surface of the medium.
Conventionally, a method for manufacturing a laminated material enclosing a transfer layer includes the following manufacturing steps. First, a transfer layer is affixed to a first sheet through a transfer process typically using thermal pressure. Then, a second sheet is directly affixed to the first sheet so that the second sheet is fused to the first sheet. Alternatively, the second sheet is affixed to the first sheet through an adhesion layer so that the second sheet is bonded to the first sheet.
The manufacturing steps described above have a number of problems. To fuse the second sheet to the first sheet, a temperature and a pressure that are higher than those used in the transfer of a transfer layer are typically applied for a long time.
This lengthy application of a high temperature and pressure during the lamination process may damage or deform the enclosed transfer layer to an extent that impairs the function of the transfer layer. To avoid this problem, the enclosed transfer layer needs to be made of a material that has a high melting point or rigidity so as not to be damaged by the temperature and pressure generated in the lamination process.
However, when the material of the transfer layer has a melting point or rigidity that is high enough to resist the thermal pressure in the lamination process, a problem occurs when affixing the transfer layer to the first sheet. That is, the high melting point or rigidity of the material may result in transfer burrs and chipping in the transfer process to the first sheet, hindering the transfer of the expected shape. The transfer burr is a section extending outward of the outline of the expected shape, and the chipping is a section extending inward of the outline of the expected shape.
This problem is particularly pronounced in the lamination process when the materials of the first and second sheets are polycarbonate materials having a higher melting point than the PVC material or amorphous copolyester material. The temperature required to laminate the polycarbonate materials having high melting points is between 170° C. and 200° C., and the lamination requires a time period of about 1 to 30 minutes.
To minimize damage to the transfer layer in the lamination process, Japanese Patent No. 4925543 proposes a method in which a transfer layer is divided into dots or lines of less than or equal to 5 mm and placed on a sheet.
However, dividing a transfer layer into minute portions and arranging them as described in Japanese Patent No. 4925543 is extremely difficult. The smaller and the more complex the shape of the transfer layer to be transferred, the more frequent the generation of transfer burrs and chipping becomes. To minimize transfer burrs and chipping, the material of the transfer layer needs to be brittle and easy to break. However, the transfer layer having such a material tends to break in the lamination process, increasing the possibility that the enclosed transfer layer is damaged or deformed to an extent that impairs the function of the transfer layer.